Issue with asset attributes (and also editor state) being reset


We are having repeated issues with attributes that reference assets being reset to ‘empty’. For example we added the following attributes yesterday:

UiStyle.attributes.add('levelSelect'        , { type: 'asset', title: 'Level Select'           });
UiStyle.attributes.add('levelSelectHover'   , { type: 'asset', title: 'Level Select - Hover'   });
UiStyle.attributes.add('levelSelectPressed' , { type: 'asset', title: 'Level Select - Pressed' });

It was working fine, and first thing this morning when we started working on the project we were met with this error:

common-ui.js:307 Uncaught TypeError: Cannot read property 'getFileUrl' of null
    at script.UiStyle.injectPauseStyle (common-ui.js:307)

Inspecting the entity in the editor revealed that this was again one of the instances where the values were reset:

There is another case where the one script is still showing attributes that we removed ages ago, this is a screenshot from this morning:

After hitting the parse button the script correctly updates (we removed all attributes - and as a rule no longer use attributes on this script):